Radiation transducer system with collimated beam readout of lens modulation elements

ABSTRACT

A method and apparatus for reproducing signals stored on a carrier in the form of undulations corresponding to the signals, the undulations generally being formed as a spiral groove. The undulations on the carrier are moved past a suitable radiation source, such as a light source, and the density of the radiation emanating from the undulations, which is a function of the curvature of the undulation, is detected by a suitable radiation detecting means after it passes through a suitable slit aperture arranged at a predetermined distance from the carrier surface, so that variations in the density are a function of the undulations. The undulations may be either frequency or phase modulated with respect to the signal and their amplitude can be modified as a function of their recorded wavelength in such a manner that the curved surface portions of the undulations have nearly the same focal length for all occurring wavelengths. The carrier can have at least one recording surface in which is formed a groove having a trapezoidal cross section and having its bottom surface provided with the undulations.

llnited States Patent 1191 Dickopp [45] June-18, 1974 7 RADIATIONTRANSDUCER SYSTEM VVHTH COLLIMATED BEAM READOUT LENS MODULATION ELEMENTS[75] Inventor: Gerhard Dickopp, Berlin, Germany [73] Assignee: LicentiaPatent-Verwaltungs-G.m.b.H., F rankfurt, Germany Filed: Sept. 29, 1972Appl. No.: 295,011

Related US. Application Data Continuation of Ser. No. 5,341, Jan. 23,1970, abandoned.

[30] Foreign Application Priority Data Jan. 23, 1969 52 us. (:1. ..1791004 R, 179 1003 v, 179/1004 M, 179/10041 L 1] [58] Field of Search..179/ 100.4 R, 100.4 M, .1Z.9/.1;QQ:F11.L; 1,Q0-3 Y 17816-9? ReferencesCited UNITED STATES PATENTS Williams.....

Mittell Runge Shepherd Germany 1903822 Int. Cl. Gll b 11/18 WilliamsUm'.179/10041. L

Miessner. 179/100.3

OTHER PUBLICATIONS IBM Tech. Disclosure Bulletin, Readout from ThermoPlastic Record Element, Fleisher et al., Vol. 10, No. 7,

Primary Examiner-Raymond F. Cardillo, Jr. Attorney, Agent, orFirmSpencer & Kaye [57] ABSTRACT A method and apparatus for reproducingsignals stored'on a carrier in the form of undulationscorresponding tothe signals, the undulations generally being formed as a spiral groove.The undulations on the carrier are moved past a suitable radiationsource,

such as a light source, and the density of the radiation emanating fromthe undulations, which is a function of the curvature of the undulation,is detected by a suitable radiation detecting means afterit passesthrough a suitable slit aperture arranged at a predetermined distancefrom the carrier surface, so that variations in the density are aflunctionpf the undulations. The undulations maybe either equer y orphasehiodu1ated \fithrespect to the signal and their amplitude can bemodified as a function of their recorded wavelength in ,v such a mannerthat the curved surface portions of the undulations have nearly the samefocal length for all occurring wavelengths. The carrier can have atleast one recording surface in which is formed a groove having atrapezoidal cross section and having its bottom surface, provided withthe undulations.

13 Claims, 9 Drawing Figures mmwmmw 8L8-18L148 SHEET 2 BF 3 FIG. 5

INVENTOR Gerhard D'ickopp ATTORNEYS.

RADIATION TRANSDUCER SYSTEM WITH COLLIMATED BEAM READOUT OF LENSMODULATION ELEMENTS CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation of application Ser. No. 5,341, filed Jan.23rd, 1970, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a systemfor reproducing signals which are stored on a record carrier in the formof spatiral undulations corresponding to the signals, the signalsbeingreproduced by means of a pickup composed of a suitable source ofradiation, such as light, and a radiation receiver.

The present invention, concerns a recording process and arrangement, areproducing method and arrangement and a record carrier for storingthesignals.

According to prior art techniques for reproducing signals which arestored as deformations in the surface of a carrier, for example, asvertical or lateral undulations formed in a groove, the playback isusually carried out by mechanical scanning employing a stylus moving inthe groove. This stylus transmits the movements imparted to its tip bythe undulations to an electromechanical transducer whose electricaloutput is a reproduction of the stored signals. With this type ofscanning, the forces, producing the mass acceleration of the moveabletransducer components, which forces increase linearly with signalfrequency and amplitude, must be transmitted directlyfrom the surfaceportions carrying the recorded signals to the tip of the scanningstylus. This not only results in increased wear, which increases withthe frequency, amplitude and the relative speed of the components movingagainst one another, but also gives rise to difficulties due to the massinertia of the moveable transducer components, limits increases in thesignal frequency range in the direction of high frequencies.

Methods have, already been proposed for scanning recording elements withthe aid of light or comparable radiation. In these cases, therecordingtechnique employed is either one in which the signals are recorded onthe surface of a carrier, or recording element, as a track more or lessdarkened according to the recorded signal, in the manner of avariable-density sound motion-picture film recording system, or in theform of areas blackened to the same degree and configured in the mannerof a variable-area optical sound motionpicture film recording system.The amount of light passed or reflected depends onthe degree ofdarkening of the carrier portions on which the reading beam impinges,and this amount of light excites a light receiver whose electric outputvalue forms a reproduction of the signal.

These methods have the disadvantage that copies of the recordingelements can be obtained only by photochemical or similar processes, andnot by simple stamping or pressing processes, such as used tomanufacture phonograph records.

It is also known in the art to use optically scannable recordingelements which contain the recorded signals in the form of surfacedeformations or undulations. It has been a major difficulty with thesesystems, however, to establish an unequivocal relationshipbetween theamount of light reflectedby the surface and the magnitude and type ofundulations. For this reason,

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a type of scanning which is free of mass inertia limitations andin which the scanning process itself does not produce any mechanicalstresses on the surfaces carrying the recorded signals, whilemaintaining the advantages of a copying process which can avail itselfof the known stamping or pressing techniques employed for manufacturingphonograph records.

This object is accomplished according to thepresen invention byproviding a light scanning system which is simple and effective, andwhich also assures a good utilization by the light receiver of thereflected or re fracted light.

A system according to the present invention employs a recording element,or record carrier, having a surface provided with undulationscorresponding-to the signal. These undulations are evaluated by means oflight or comparable radiation acting on a radiation receiver. A slitaperture is disposed in the path of a reading beam and at such adistance from the undulations that a change in the density of theradiation emanating from the undulations occurs in the plane of the slitaperture. This density is dependent on the curvature of theundulationsin the direction of movement of the carrier with respect tothe reading beam,-and the changes in the density at least qualitativelyfollow the curvature variations. The signal is recorded in the form of acarrier undulatio'n which is frequency or phase modulated in accordancewith the signal.

' In preferred embodiments of the present invention, the undulationscontaining the recorded signals constitute convex or concave lenses ormirror surfaces. These lenses or mirror surfaces density modulate thereading beam, which is preferably a collimated beam, in the plane of theslit aperture in a manner corresponding to the variations inthe-curvature of the undulation surface. This density modulation is thusat least a qualitative representation of the surface curvature and is afunction of the well known laws of reflection and refraction. Forexample, in the case of light passing through the record carrier, aconvex surface increases, and a concave surface decreases, the lightdensity in the plane of the slit aperture. A similar result is obtainedwhen light is reflected from a mirror surface on the record carrier. Inthe case of reflection, a concave surface produces a converging effectwith an increase in the lightdensity, and a convex surface diverges thelight to produce a decrease in the light density, in th plane of theslit aperture.

In order to maintain the distance between the record carrier and theplane of maximum convergence of the light originating from the readingbeam substantially constant, the system according to the presentinvention a signal is recorded by frequency or phase modulating acarrier as a function of signal. This causes the wavelengths of theundulations containing the recorded signals to vary over a smaller rangethan would occur in the direct recording of the-low frequency, widebandwidth signal, If an arbitrary audio frequency signal were directlyrecorded in the undulations, the wavelengths and amplitudes of theundulations making up the complex signal would vary over a large range.Generally, this would result in different curvatures and, thus,different focal lengths, for the cylindrical lenses or mirrors, definedby the undulation surface so that the plane of maximum convergence ofthe radiation emanating from the reading beam would lie at differentdistances from the plane representing the average undulation depth fordifferent undulation wavelengths or amplitudes.

Recording of the signal by frequency or phase modulation of a carrieroscillation, according to the present invention, makes it possible toprovide undulations having an approximately constant amplitude and areduced wavelength range. Under these circumstances, it ispossible toselect a certain, predetermined optimum distance for the plane of theslit aperture from the center surface,or average undulation depth, planeof the record carrier.

A recording process is also provided, according to the presentinvention, in which the amplitude of the recorded carrier, which isfrequency or phase modulated with the signals and recorded asundulations on the recording surface, is varied as a function of theundulation wavelength. This feature of the invention serves the purposeof maintaining approximately a constant focal length for the cylindricallenses or mirrors for the entire wavelength range of the recordedundulations. If, in contrast the wavelength were to be reduced whilemaintaining the undulation amplitude constant, the curvature of thesurface portion would be increased and, thus, a shortening of the focallength would result. This change is counteracted by a correspondingchange in amplitude.

A particular advantage of the system according to the present inventionover other systems employing lightscanning is that an appropriateselection of the focal plane location leads to a larger peak-to-peakvariation in the amount of light passing through the scanning slitaperture. This results in a better signal to noise ratio.

The present invention also provides the possibility to record a verywide signal frequency band. This band may extend into the megahertzrange on a record carrier fully comparable to a phonograph record.Another advantage of the present invention is that the record carriermay be duplicated by hot pressing a thermoplastic mass. This duplicationmethod is well known in the phonograph record art, and permits theproduction of records containing, for example, television signals andeven including information to be reproduced in color.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic, side elevationview of an embodiment of a system according to the present invention inwhich a surface. of a recording element is scanned with the aid of areading beam passing through the carrier.

FIG. 2 is a schematic, side elevational view showing a portion of thedevice of FIG. 1 on a much larger scale.

FIG. 3 is a schematic, side elevational view similar to FIG. 2, butshowing an embodiment of the present invention where the light isreflected from the surface the carrier or recording element.

FIG. 4 is a perspective view, partially in cross section, showing aportion of a recording element having a groove whose bottom surfacecontains undulations.

FIG. 5 is a schematic, side elevational, crosssectional view of aportion of a recording element having a plurality of parallel grooveswhose bottom surfaces are inclined with respect to a plane normal to theimpinging reading beam.

FIG. 6 is a side elevational, cross-sectional view of a recordingelement having undulations in the form of cylindrical lenses havingidentical radii of curvature.

FIG. 7 is a side elevational, cross-sectional view of a recordingelement having undulations in the form of cylindrical parabolic mirrorswhose lines of intersection with the plane of the drawing all formportions of the same parabola.

A suitable synthetic foil material is e.g. polyvinychloride orpolystyrene.

FIG. 8 shows a cutting system and the necessary signal processingcircuitry for cutting grooves having the configurations shown in FIGS. 6and 7.

FIG. 9 shows an optical reading system and a pickup guided by groovewalls.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circular,disc-shaped carrier, or recording element 1, which is provided withsurface undulations corresponding to the time sequence of the signalvalues; the undulations also corresponding to the system of theinvention. This recording element 1 is assumed to be disposed on asupport (not shown), such as a conventional turntable which may betransparent if necessary, by means of which it can be rotated in thedirection of the arrow about its axis 2 which is perpendicular to thelarge-area surfaces of the carrier 1. The turntable and consequently therecording element 1 can be rotated by any conventional drive meansindicated schematically in FIG. 1. FIG. 1 is directed to a preferredembodiment, where the recording element 1 consists of a suitable foilmaterial, such as a synthetically produced plastic.

The recording element I is penetrated by the reading light rays 3, whichemanates from a suitable, wellknown light source 4. By means of asuitable optical arrangement associated with the light source 4, care istaken that the reading light rays '3 consist substantially of parallelrays of light, forming a reading beam 5. The reading beam 5 penetratesinto the material of the recording element, from the generally planarunderside thereof, which is perpendicular to the axis of the beamwithout any appreciable deflection of the individual rays. The uppersurface of recording element 1 is provided with the spatial deformationsin which the recorded signal is stored. When the rays emerge from thesurface they are refracted to a degree depending on the angle which thesurface forms with respect to the beam. This effect will be explainedlater in detail with reference to FIG. 2. The light refraction in acylindrical lens convex toward the top. which is present on the surfaceof the carrier I, results in a convergence of the light; refraction in acylindrical lens which is concave toward the top results in divergenceof the light. It is here presupposed that carrier 1 is transparent inthe area of the surface bearing the deformations and is disposed in thepath of preferably parallel light rays between the light source 4 andthat plane 6 in which rays collected by a quasi-cylindrical lens'on itssurface are optimally converged by the lens.

The greatest changes in light density also result in this plane whensurface portions of recording element 1 having'different curvatures passthrough the area of reading beam 5. These changes in light density areutilized by a suitable optic, such as a double-convex lens 7 of thearrangement according to FIG. 1, in cooperation with a receiving slit 8,which maybe similar to the well-known mechanical slit in optical filmsound reproducing systems, and a conventional radiation receiver 9, suchas a photoelectric cell. Experiments and calculations have shown'thatthe plane at which occur the changes in light density sensed by theradiation receiver 9 should be spaced from the median surface plane 12of carrier 1, when based on cylindrical lenses whose lines ofintersection with a plane perpendicular to the cylinder axis are sinecurves, by a distance somewhat greater than the distance between plane12 and that plane in which the beams near the axis of symmetry of theoptical arrangement formed by surface portions curved in themanner ofcylindrical lenses or mirrors are maximally concentrated.

In the case of a reading beam with parallel rays, as is presupposed inFIG. 1, the concentration of the rays at or near the axis of symmetry ina plane passing through the principal focus of the cylindrical lensesshould be expected. The rays somewhat offset from the axis of symmetry,are not brought to a focus in this focal plane but, for a sinusoidallens element, are converged somewhat therebehind. Thus, the plane ofoptimum light density variation lies, in this case, somewhat behind theprincipal focal plane.

If, however, cylindrical deformations having a circular cross sectionwere used, the rays which are offset from the plane of symmetry wouldalso converge almost in the principal focal plane and the twoabovementioned planes would practically coincide. It should bepresupposed that the plane 6 shown in FIG. 1 forms that plane in whichmaximum light density variations result in both cases.

With the aid of an optical arrangement 7 which is schematically shown inFIG. 1 as a double convex lens, the plane 6, in which there may bedisposed the light receiver and a receiving slit, is reproduced orimaged, in plane 11, where there is disposed a receiving slit aperture 8which is spaced from plane 6 along the optical axis. This arrangementhas the advantage that the slit 8 need not be disposed within plane 6,i.e. in direct spatial proximity to the surface of carrier 1. The use ofan auxiliary optical arrangement 7 also has the advantage that it ispossible to reproduce plane 6in slit plane 11 to an enlarged scale. Thismakes it possible to dimension the slit aperture 8 in the direction ofthe relative velocity of the carrier with respect to the reading beami.e. the length 1 of the slit, somewhat larger than if the slit aperturewere disposed directly in the plane 6. It has been found that the lengthof the slit should be selected to be approximately equal to half, orless than half, the shortest wavelength of the carrier oscillations tobe recorded, this dimension being with reference to plane 6. The slitlength in plane 11 may be selected to be different, depending on thedegree of enlargement, and is marked 1'. In FIG. 1 the beam pathstarting from the reading beam 5 is illustrated with solid lines for thecase of penetration through plane surface portions. The dot-. dash linesshow the ray path of the optical arrangement 7 for reproduction of plane6 in plane 11 of the slit aperture 8.

FIG. 2 shows, to an enlarged scale, a portion of carrier 1 of FIG. 1which is penetrated by the reading beam 5. The illustration is asectional view parallel to the rays of reading beam 5 and in the planeof the relative speed of carrier 1 with respect to the axis of thereading beam. FIG. 2 shows undulations 10 containing the recordedsignals on the upper side of carrier 1. Mirror-like, reversedundulations can also be disposed on the underside of carrier 1 (notshown). This ,would increase the lens effect of the deformations but theeffect could only be optically utilized when carrier 1 is in the form ofa foil whose thickness is not being substantially less than twice theamplitude of undulations 10. Only in'such a case could there be a usefulcooperation of the curvatures on the upper side and the underside of thefoil.

The undulations on the upper side of the carrier form quasi-cylindricallenses which represent convex lenses above the surface center line 12 ofcarrier 1 and concave lenses therebelow. Their line of intersection withthe plane of the drawing is assumed-to be a sine curve.

The ray paths shown with arrows indicate'that the rays of reading beam 5remain parallel until they emerge from the surface provided withundulations 10. In the area' of the rays adjacent to the axis ofsymmetry 13 of a convex cylindrical lens, there occurs an intersectionof the rays at the focal point plane 17. The rays further away from theaxis of symmetry 13 do not intersect exactly in this plane in the casecylindrical lenses having sinusoidal profiles. Instead, they converge inthe plane of optimum light density variation slightly behind the focalpoint plane 17, which plane of optimum light density variation is markedwith the reference numeral 6 in FIGS. 1 and 2. In this plane, therefore,as illustrated, there should be'disposed the slit aperture 8 of theradiation receiver 9 when cylindrical lenses of the above-mentioned sineshape are being used. With cylindrical lenses having circular lines ofintersection, planes 6 and 17 practically coincide.

In the area of the undulations 10 disposed below the surface center line12, which areas form a concave lens, there is produced a divergence ofthe beam. Thus, at these points in planes 17 or 6, respectively, thelight densities are reduced with respect to that of the collimated beam5.

If carrier 1 is now moved relative to the axis of the reading beam 5 ata relative speed in the direction of the center line 72 in FIG. 2, thelight density in plane 6 assumes variable values independence on thecurvature ,of the undulations 10. This is a qualitative representationof the curvatures of these deformations insofar as a positive curvature,or convex lens, corresponds to an increase in light density and anegative curvature, or concave lens, correspond to a decrease in lightdensity. This relationship further provides information about thequantitative changes in the curvature, since the functions of the lightdensity changes and the curvatures are so associated with one anotherthat changes in the same sense in one function always correspond to suchchanges in the other function. It would thus be possible to scandirectly recorded audio frequency signals in this manner, wherefrequencies and amplitudes would be reproduced, but the effect of thevaried wavelengths and' the varied amplitudes would here be annoyingbecause this would result in changes of the focal point distance. Thesechanges are reduced to a substantial degree by the recording techniqueemployed in the present invention where the signal values are recordedas frequency or phase modulated carrier oscillations, and they can bepractically entirely eliminated by modulation simultaneously with achange in the amplitude.

Calculations have shown that when the deformation of the recordingsurface approximates a sinusodial path when viewed in a planeperpendicular to the plane of the center surface of the recordingelement and parallel to the direction of the relative speed between therecording element and the reading beam bundle in the proximity of thescanning range, the following relation should be approximatelymaintained for the change in amplitude as a function of the wave lengthin order to keep the change in focal length as small as possible;

where A is the amplitude, k=2rr/2\ the number of waves (It wavelength),y is the clistarice to the focal plane and n is the index of refractionof the material used for the recording element. Optically, a sinusoidalpath in the plane of the recording element referred to above is not themost favorable, but it is preferred because it is easily produced.

When scanning a disc-shaped carrier according to the system of thepresent invention, difficulties might occur due to disc wobble. This iscaused by the carrier surface not being exactly perpendicular to theaxis of rotation 2, by deviations of the surface of the carrier 1 fromone plane. When disc wobble occurs, the resulting angle between theimpinging reading beam and the groove in its direction of movement thencauses the point illuminated by the reading beam to move along thatdirection. This simulates an additional frequency modulation which mightlead to scanning distortions. In a preferred embodiment of a playbackarrangement for the system according to the present invention, it isprovided that the reading beam is directed to impinge on the carriersurface parallel to the axis of rotation 2 of the discshaped carrier 1.In this manner the so-called up-and-down wobble of the carrier surfacedoes not lead to displacements of the currently scanned surface elementsin the direction of the relative speed, and only partial lengths withinthe beam path change to a slight degree.

FIG. 3 shows an enlarged view of carrier 1 for the case of reflection ofthe reading beam 5 from the surface of the carrier bearing theundulations At first glance, this arrangement seems to be more difficultto realize in practice because now the light source 4 and the radiationreceiver 9 must be disposed on the same side of the carrier. As will beshown later on, however, this difficulty can be substantially overcomeby additional measures.

In the arrangement according to FIG. 3, the rays of reading beam 5 whichare reflected by the concave mirrors disposed below the surface centerline 12 intersect at the focal plane 14 at which there may also bedisposed the slit aperture 8 (see FIG. land 2) and which corresponds toplane 17 of FIG. 2. The distance of this plane from the surface centerline 12, however, is less for the reflection from the undulations 10, asshown in FIG. 3, than it would be for the case of refraction uponirradiation of the carrier according to FIG. 2. In the case ofreflection according to FIG. 3, the distance of the plane of optimumlight density variations from the surface center plane 12 is alsosomewhat larger, when undulations with sine-shaped lines of intersectionare used, than the distance of the focal plane 14 from the same surfacecenter plane. The undulations 10 disposed above the surface center plane12 cause in the arrangement according to FIG. 3, a divergence of thelight. When the carrier 1 passes under reading beam 5 there resultchanges in the light density in the focal plane 14, or in a planeparallel thereto, which represent a reproduction of the curvatures ofthe surface portions bearing undulations 10 and which can be madeeffective by a slit aperture with a light receiver disposed in one ofthese planes.

In order to effect as good a reflection as possible of the rays of beam5 at the surface of the carrier, carrier 1 may advisably be providedwith a reflective coating in the area of the surface bearing theundulations 10 so that then the light emanating from the light source isconverged by reflection into a plane 14 disposed on the same side as thelight source. A suitable material to be used as a reflective coating ise.g. aluminum or silver.

A further development of the present invention relates to a carrier fora recording method according to the system of the present invention, inwhich the undulations 10 are disposed on the bottom surface of a groovehaving a trapezoidal cross section and where the axes of thequasi-cylinders are disposed transverse to the direction of the groovecenter line. A portion of such a carrier is shown in FIG. 4.

The groove 15 has two sides 15' and bottom surface 16 which is firstintended to be unmodulated. In the modulated state, as it is shown inFIG. 4, the bottom surface 16 bears the undulations 10 which form thesignal recording. In a playback arrangement, the groove sides 15' may beused for the engagement of an auxiliary means for mechanically guidingthe optical pickup. This auxiliary means need not come in contact withthe bottom surface 16 of the groove, however. This bottom surface israther evaluated in the above-described manner by its influence on theray path of the reading beam 5.

FIG. 5 shows a section through a portion of a carrier 1 on which thereare disposed a spiral groove, several turns of which are shown, having atrapezoidal cross section. The sectional view is shown perpendicular tothe groove center lines. In order to facilitate the ar' rangement of thelight source 4 and of radiation receiver 9 on the same side of thecarrier for the case of reflection from the carrier surface, the bottomsurface 16 of the groove, which is imagined to be still unmodulated, isso disposed that it forms an angle other than with the axis of thereading beam 5. In FIG. 5 the lines provided with arrows indicate theaxis of the reading beam 5 which is directed onto the associated bottomsurface 16 of the groove. The impinging portion of the radiation is heredirected, as presupposed, to be parallel to the axis of rotation 2(FIG. 1) whereas the reflected portion of the beam now forms an acuteangle with the impinging portion. This acute angle offers sufficientroom for the accommodation of the radiation receiver 9 adjacent the pathof the impinging beam.

Thus far, it has been assumed that the line of intersection of thesurface bearing a quasi-cylindrical undulation, e.g. of surface 16 inFIG. 4, with a plane perpendicular to the surface center plane 12 and,containing the direction of the relative speed between carrier 1 andreading beam 5 in the scanning region is a sine wave, because suchundulations directly correspond to the time sequence of a sinusoidalcarrier oscillation and, thus, can be produced on a master with knownmeans by a simple cutting process. However, the resultingquasicylindrical lenses or quasi hollow mirrors, re spectively, do notprovide the optimum convergence of parallel beams in a certain focalplane. A better convergence results, according to a further developmentof the present invention, when the above-defined line of intersection isdesigned to be other than sine-shaped, and is approximately circular inthe top and/or bottom portions. These portions are approximatelycircular in the case of refraction and are approximately paraboloid inthe case of reflection. This configuration can be achieved in a simplemanner by incorporating appropriate distorting members in the path ofthe recording amplifier, for example when the sine oscillation isrecorded after a full wave rectification. For the case of refraction,this results in optical conditions which are related to those which areknown for spherical lens systerns when the beam path is considerd withinone axial plane. For'the case of reflection, the conditions which resultare thoseknown from observations with parabolic mirrors. With thesefurther developments it is thus possible to achieve furtherimprovements'in the convergence of the ray path, so that the relativechanges to the light density in the plane utilized by the radiationreceiver become even greater, and abetter signal-to-noise ratio isachieved.

FIG. 6 shows an enlarged view of a portion of a carrier 1 provided withundulations on its surface which, according to the above-mentionedfurther development of the present invention, form portions ofcircularly cylindrical lenses, all having the same radius R. The widthsof the lens portions between b and b,,,,-,, are different from oneanother, however, such that the desired frequency or phase modulation ofthe light density changes effected in the focal plane results. Thecarrier shown in FIG. 6 is used in the same manner as the type discussedin connection with FIG. 2 for the light irradiation when plane 6approximately coincides with plane 17. This would be. exactly so if thetop portions of the illustrated lenses were at the same distance fromthe focal point plane.

FIG. 7 is an enlarged view of a portion of a carrier 1" which isprovided with undulations 10 on its surface, which form portions ofcylindrical parabolic hollow mirrors whose lines of intersection withthe plane of the drawing are constituted by the same parabola for allmirror-portions of different widths. That is, they all have the sameequation of curvature. Accordingly, the focal lengths are alsoidentical. Their length is, as is the length of the cylinder lensportion of FIG. 6, between b and b,,,,-,,. The changes in length providethe desired frequency or phase modulation. The correct selection of thefocal plane, causes a larger variation in the .proportion of the lightbeam passing through the scanning slit. This results in a better signalto noise ratio.

Calculations have shown that these light density fluctuations aremaintained over a relatively great distance range for the slit aperture8 with respect to the surface center plane 12, so that the requirementsforthe verti-, cal adjustment of the slit aperture 8 and the radiationreceiver 9 with respect to the carrier surface are simpli fied. If, asshown in FIG. 1, the optical system 7 is employed to reproduce the planeof strong light density fluctuations in the plane of the slit aperture,this requirement is correspondingly reduced with respect to maintenanceof the depth of field. Surface irregularities or variations in thesurface height during rotation of carrier 1 on the playback apparatusdue to disc wobble are therefore less of a problem than in' knownlightscanning processes.

FIG. 8 shows a block diagram of the recording system and the necessarysignal processing circuitry. The frequency or phase modulated signal islimited in the limiter 18 and the limited signal is differentiated bythe differentiating network 19. The needle pulses occurring at theoutput of the differentiating network control alternately two functiongenerators 21 and 22 by a flip-flopcircuit 20. The function generatorsproduce equal signals of circular or parabolic shape. The comparatorcirnected to a transparent body 28 e.g. of diamond. The

pickup is sliding in a groove 15. With the aid of the convex lens 7 theplane 6 in FIG. 1 is reproduced in plane 11, where there is disposed thereveiving slit aperture 8 and above it the light receiver 9.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim: I

1. An apparatus for reproducing signals stored on a recording carrier ina recording track in the form of surface undulations corresponding tothe time sequence of the signals, the surface undulations having theform of cylindrical density modulating surfaces with axes disposedtransversely to the recording track, comprising, in combination:

a. radiation means which emits radiation in the form of an approximatelycollimated beam toward a portion of the surface undulations to cause thecollimated beam to impinge upon the undulations so as to be modulated bythe surfaces thereof in a mannet to cause, at a plane parallel to andspaced a given distance from the carrier surface, the density of theradiation emanating from the undulations to be a function of thecurvature of the density modulating surfaces;

b. means for driving the recording carrier relative to the radiationsource in the direction of the track;

c. a radiation receiver disposed for receiving theradiation emanatingfrom the surface undulations;

d. a slit aperture means disposed in the beam path between the region tobe occupied by the surface undulations and the radiation receiver; and

e. optical means disposed in the beam path between the surfaceundulations and said slit aperture means for reproducing the plane whichis a given distance from the carrier surface at the slit aperture planesaid slit aperture means having an aperture which has a lengthtransverse to the cylinder axes and in the direction of the relativemovement of the recording carrier with respect to the radiationreceiver, said length being less than the product of the shortestwavelength of the surface undulations and the enlargement factor of theoptical means.

2. A method for reproducing a signal stored on a carrier having asurface with a series of undulations arranged along a recording trackand corresponding to a function of the time behavior of said signal, theundulations constituting cylindrical radiation density modulatingsurfaces whose cylinder axes lie substantially perpendicular to thedirection of the recording track, comprising the steps of: I

a. causing a substantially collimated beam of radiation to impinge uponsaid undulations so as to be modulated by'the surfaces thereof in amanner to cause, at a plane parallel to and spaced a given distance fromthe carrier surface, the density of the radiation emanating from theundulations to be a function of the curvature of the density modulatingsurfaces;

b. arranging a slit aperture means in such plane, said aperture meanshaving a length, transverse to the cylinder axes and in the direction ofthe relative movement of the carrier with respect to said radiation,which is less than the shortest wavelength of the surface undulations;

c. moving the carrier relative to said radiation in the direction ofsaid track; and

. detecting the density of the radiation emanating from the undulationsthrough said slit aperture means, the density of the radiation emanatingfrom the undulations changing in dependence on the curvature of thedeformed surfaces of the undulations in the direction of the relativespeed of the carrier with respect to the impinging radiation so that thechange in density reproduces the path of the undulations at leastqualitatively.

3. A method as defined in claim 2, wherein the undu lations are formedto approximate a frequency modulated oscillation.

4. A method as defined in claim 2, wherein the undulations are formed toapproximate a phase modulated oscillation.

5. A method for reproducing a signal stored on a carrier having asurface with a series of undulations arranged along a recording trackand corresponding to a function of the time behavior of said signal, theundulations constituting cylindricalradiation density modulatingsurfaces whose cylinder axes lie substantially perpendicular to thedirection of the recording track, comprising the steps of:

a. causing a substantially collimated beam of radiation to impingeupon-said undulations so as to be modulated by the surfaces thereof in amanner to cause, at a plane parallel to and spaced a given distance fromthe carrier surface, the density of the radiation emanating from theundulations to be a function of the curvature of the density modulatingsurfaces;

b. optically reproducing such plane at a reproduction plane by opticalmeans having a given enlargement factor; V

c. arranging a slit aperture means in the reproduction plane, saidaperture means having a length, transverse to the cylinder axes and inthe direction of the relative movement of the carrier with respect tosaid radiation;

d. moving the carrier relative to said radiation applying device; and

e. detecting the density of the radiation emanating from the undulationsthrough said slit aperture means, the density of the radiation emanatingfrom the undulations changing in dependence on the curvature of thedeformed surfaces of the undulations in the direction of the relativespeed of the carrier with respect to the impinging radiation so that thechange in density reproduces the path of the undulations at leastqualitatively.

6. A method as defined in claim 5, wherein the undulations are formed toapproximate a frequency modulated oscillation.

7. A method as defined in claim 5, wherein the undulations are formed toapproximate a phase modulated oscillation.

8. An apparatus for reproducing signals stored on a recording carrier ina recording track in the form of surface undulations corresponding tothe time sequence of the signals, the surface undulations having theform of cylindrical density modulating surfaces with axes disposedtransversely to the recording track, comprising, in combination:

a. radiation means which emits radiation in the form of an approximatelycollimated beam toward a portion of the surface undulations to cause thecollimated beam to impinge upon the undulations so as to be modulated bythe surfaces thereof in a manner to cause, at a plane parallel to andspaced a given distance from the carrier surface, the density of theradiation emanating from the undulations to be a function of thecurvature of the density modulating surfaces;

b. means for driving the recording carrier relative to the radiationsource in the direction of the track;

c. a radiation receiver disposed for receiving the radiation emanatingfrom the surface undulations; and

d. a slit aperture means disposed in such plane between the region to beoccupied by the surface undulations and the radiation receiver, saidaperture means having an aperture which has a length transverse to thecylinder axes and in the direction of the relative movement of therecording carrier with respect to the radiation receiver, said lengthbeing less than the shortest wavelength of the surface un dulations.

9. The apparatus as defined in claim 8, wherein the distance of saidslit aperture means from a plane representing the average mid-point ofthe undulations is selected to be somewhat greater than the distancebetween the plane where radiation emanating from the undulations isfocused and the average mid-point.

10. The apparatus as defined in claim 9, wherein the carrier has an axisof rotation, and wherein the radiation is directed parallel to the axisof rotation of the carrier and perpendicular to its surface areacontaining the undulations.

11. The apparatus as defined in claim wherein the undulations havecontinuously curved surfaces which substantially define sine curve alongthe direction of 5 relative speed between the carrier and the radiationfrom said radiation means and wherein the amplitude of the undulationschanges in dependence on the wavelength of the modulated carrieroscillation as an approximate function of the following relation:

wherein A is the amplitude, k the number of waves Zw/Mk wavelength), yis the distance between the focal plane of the radiation emanating fromthe undulation and the plane of the center surface of the carrier, and nis the index of refraction of the material used to fabricate therecording element.

12. The apparatus as defined in claim 11, wherein said undulations areconfigured as quasi-cylindrical lenses, and wherein said radiation meansis arranged so as to pass said approximately collimated beam through atransparent carrier mounted for rotation with respect to the light raysso that the rays emanating from the carrier are converged to the planewhere the rays are same side of the carrier as the light source.

1. An apparatus for reproducing signals stored on a recording carrier ina recording track in the form of surface undulations corresponding tothe time sequence of the signals, the surface undulations having theform of cylindrical density modulating surfaces with axes disposedtransversely to the recording track, comprising, in combination: a.radiation means which emits radiation in the form of an approximatelycollimated beam toward a portion of the surface undulations to cause thecollimated beam to impinge upon the undulations so as to be modulated bythe surfaces thereof in a manner to cause, at a plane parallel to andspaced a given distance from the carrier surface, the density of theradiation emanating from the undulations to be a function of thecurvature of the density modulating surfaces; b. means for driving therecording carrier relative to the radiation source in the direction ofthe track; c. a radiation receiver disposEd for receiving the radiationemanating from the surface undulations; d. a slit aperture meansdisposed in the beam path between the region to be occupied by thesurface undulations and the radiation receiver; and e. optical meansdisposed in the beam path between the surface undulations and said slitaperture means for reproducing the plane which is a given distance fromthe carrier surface at the slit aperture plane said slit aperture meanshaving an aperture which has a length transverse to the cylinder axesand in the direction of the relative movement of the recording carrierwith respect to the radiation receiver, said length being less than theproduct of the shortest wavelength of the surface undulations and theenlargement factor of the optical means.
 2. A method for reproducing asignal stored on a carrier having a surface with a series of undulationsarranged along a recording track and corresponding to a function of thetime behavior of said signal, the undulations constituting cylindricalradiation density modulating surfaces whose cylinder axes liesubstantially perpendicular to the direction of the recording track,comprising the steps of: a. causing a substantially collimated beam ofradiation to impinge upon said undulations so as to be modulated by thesurfaces thereof in a manner to cause, at a plane parallel to and spaceda given distance from the carrier surface, the density of the radiationemanating from the undulations to be a function of the curvature of thedensity modulating surfaces; b. arranging a slit aperture means in suchplane, said aperture means having a length, transverse to the cylinderaxes and in the direction of the relative movement of the carrier withrespect to said radiation, which is less than the shortest wavelength ofthe surface undulations; c. moving the carrier relative to saidradiation in the direction of said track; and d. detecting the densityof the radiation emanating from the undulations through said slitaperture means, the density of the radiation emanating from theundulations changing in dependence on the curvature of the deformedsurfaces of the undulations in the direction of the relative speed ofthe carrier with respect to the impinging radiation so that the changein density reproduces the path of the undulations at leastqualitatively.
 3. A method as defined in claim 2, wherein theundulations are formed to approximate a frequency modulated oscillation.4. A method as defined in claim 2, wherein the undulations are formed toapproximate a phase modulated oscillation.
 5. A method for reproducing asignal stored on a carrier having a surface with a series of undulationsarranged along a recording track and corresponding to a function of thetime behavior of said signal, the undulations constituting cylindricalradiation density modulating surfaces whose cylinder axes liesubstantially perpendicular to the direction of the recording track,comprising the steps of: a. causing a substantially collimated beam ofradiation to impinge upon said undulations so as to be modulated by thesurfaces thereof in a manner to cause, at a plane parallel to and spaceda given distance from the carrier surface, the density of the radiationemanating from the undulations to be a function of the curvature of thedensity modulating surfaces; b. optically reproducing such plane at areproduction plane by optical means having a given enlargement factor;c. arranging a slit aperture means in the reproduction plane, saidaperture means having a length, transverse to the cylinder axes and inthe direction of the relative movement of the carrier with respect tosaid radiation; d. moving the carrier relative to said radiationapplying device; and e. detecting the density of the radiation emanatingfrom the undulations through said slit aperture means, the density ofthe radiation emanating from the undulations changing in dependence onthe curvature of the deformed Surfaces of the undulations in thedirection of the relative speed of the carrier with respect to theimpinging radiation so that the change in density reproduces the path ofthe undulations at least qualitatively.
 6. A method as defined in claim5, wherein the undulations are formed to approximate a frequencymodulated oscillation.
 7. A method as defined in claim 5, wherein theundulations are formed to approximate a phase modulated oscillation. 8.An apparatus for reproducing signals stored on a recording carrier in arecording track in the form of surface undulations corresponding to thetime sequence of the signals, the surface undulations having the form ofcylindrical density modulating surfaces with axes disposed transverselyto the recording track, comprising, in combination: a. radiation meanswhich emits radiation in the form of an approximately collimated beamtoward a portion of the surface undulations to cause the collimated beamto impinge upon the undulations so as to be modulated by the surfacesthereof in a manner to cause, at a plane parallel to and spaced a givendistance from the carrier surface, the density of the radiationemanating from the undulations to be a function of the curvature of thedensity modulating surfaces; b. means for driving the recording carrierrelative to the radiation source in the direction of the track; c. aradiation receiver disposed for receiving the radiation emanating fromthe surface undulations; and d. a slit aperture means disposed in suchplane between the region to be occupied by the surface undulations andthe radiation receiver, said aperture means having an aperture which hasa length transverse to the cylinder axes and in the direction of therelative movement of the recording carrier with respect to the radiationreceiver, said length being less than the shortest wavelength of thesurface undulations.
 9. The apparatus as defined in claim 8, wherein thedistance of said slit aperture means from a plane representing theaverage mid-point of the undulations is selected to be somewhat greaterthan the distance between the plane where radiation emanating from theundulations is focused and the average mid-point.
 10. The apparatus asdefined in claim 9, wherein the carrier has an axis of rotation, andwherein the radiation is directed parallel to the axis of rotation ofthe carrier and perpendicular to its surface area containing theundulations.
 11. The apparatus as defined in claim 10 wherein theundulations have continuously curved surfaces which substantially definesine curve along the direction of relative speed between the carrier andthe radiation from said radiation means and wherein the amplitude of theundulations changes in dependence on the wavelength of the modulatedcarrier oscillation as an approximate function of the followingrelation: A yB/2 - Square Root yB2/4 - 1/(n-1)k2 wherein A is theamplitude, k the number of waves 2 pi / lambda ( lambda wavelength), yBis the distance between the focal plane of the radiation emanating fromthe undulation and the plane of the center surface of the carrier, and nis the index of refraction of the material used to fabricate therecording element.
 12. The apparatus as defined in claim 11, whereinsaid undulations are configured as quasi-cylindrical lenses, and whereinsaid radiation means is arranged so as to pass said approximatelycollimated beam through a transparent carrier mounted for rotation withrespect to the light rays so that the rays emanating from the carrierare converged to the plane where the rays are focused by the refractivepower of said undulations.
 13. The apparatus as defined in claim 11,wherein said undulations are configured as quasi-cylindrical mirrors,and wherein said radiation means is arranged to reflect saidapproximately collimated beam off of a relative coating in the area ofthe carrier bEaring the undulations so that the light rays reflectingfrom the undulations are converged in a plane arranged on the same sideof the carrier as the light source.